Automotive vehicles and small vessels use D.C. electrical power sources for operation of lights and controls; the traditional power source for these applications was a DC generator driven from the vehicle engine. More recently, with major improvements in rectifier technology, the DC generator has been replaced by the combination of a small alternator and a rectifier. The most practical and most widely used type of alternator employs a rotating field, using a magnetic core usually manufactured by a combination of forging and machining operations.
Thus, one traditional practice followed in manufacturing the magnetic core members used in rotating-field alternators intended for use in automotive vehicles and small vessels has begun with a segment of low-carbon steel bar stock, which is initially forged to a general approximation of the desired external configuration for a rotor core member. After the initial forging operations the resulting core blank is de-burred and then may be subjected to additional forging to obtain a closer approximation of the required configuration for the rotor core member. The core blank is then machined to cut a shaft-mounting aperture through the hub of the core blank and to finish a number of surfaces on the core blank, surfaces that require close tolerances. Finally, additional de-burring is usually required to complete the machining procedures.
Another traditional manufacturing process is a stamping method, in which a core blank is punched out of a segment of steel plate and mechanically bent to have a close approximation of the required configuration for the rotor core member, which then may be subjected to machining and deburring to obtain adequate dimensional precision. The present invention, however, is more closely related to the forging process described above.
The machining operations usually employed in the manufacture of a magnetic rotor core member constitute a major part of the cost of manufacture. Nevertheless, close-tolerance finish machining procedures have been considered essential to the manufacture of rotor core members of adequate quality. The same basic problems are presented in the manufacture of magnetic rotor core members for other dynamoelectric machines (e.g. motors) of similar type and size.